a = input()
if 10000 > int(a) > 999:
    v1, v2, v3, v4 = a[0], a[1], a[2], a[3]
    f = [int(v1), int(v2), int(v3), int(v4), int(v1+v2), int(v2+v3), int(v3+v4), int(v1+v2+v3), int(v2+v3+v4), int(v1+v2+v3+v4)]
    b = 0
    e = []
    for c in f:
        b = 0
        for d in range(2, c - 1):
            if c % d == 0:
                b = 1
        if b == 0:
            e.append(c)      
    if len(e) > 0:
        print(max(e))
    else:
        print(0)
else:
    print(0)
